1. Field of the Invention
Embodiments of the present, disclosure relate to planar antennas that may be disposed on printed circuit boards (PCBs) or other substrates. More particularly, the present disclosure relates to a planar tunable inverted-F antenna (IFA).
2. Discussion of Related Art
Security or alarm systems are installed in premises to detect hazardous or potentially hazardous conditions. A security system generally includes a plurality of detectors/sensors, one or more keypads, and a control panel which contains the system electronics and may include a communication interface (communicator) for remote monitoring and two-way communication over telephone or wireless communication paths. Each of the detectors communicates with the control panel to provide notification of an alarm condition. Examples of possible alarm conditions include unauthorized entry or the unexpected presence of a person who may be an intruder, fire, smoke, toxic gas, high/low temperature conditions (e.g., freezing), flooding, power failure, etc. In other words, an alarm condition may represent any detectable condition that might lead to personal hazard or property damage. Audible and/or visible alarm devices such as sirens, lights, etc., may also be utilized to notify occupants of the existence of an alarm condition. The control panel may be located in a utility room, basement, etc., and may communicate with the detectors and notification devices by wired, wireless or alternative signal paths. A keypad, which may also communicate with the control panel via a wired or wireless connection, is used to arm/disarm the system as well as to provide a means to display various system messages via a status display screen. In certain designs, the keypad and control panel may be integrally housing within a single unit.
FIG. 1 is a block diagram of a security system 10 installed in a building or premises. Security system 10 includes a control panel 20 which generally controls operation of the system. A number of detection devices 181 . . . 18N are utilized to monitor an area. Detection devices may include, for example, motion detectors, door contacts, glass break detectors, smoke detectors, water leakage detectors, gas detectors, etc. Detection devices 181 . . . 18N communicate with panel 20 by a dedicated wired interconnect 18A, wirelessly 18B, through the electric (i.e. power) wiring of the premises 18C, or otherwise. One or more user interfaces, such as keypad 25 is used to communicate with control panel 20 to arm, disarm, notify and generally control system 10.
Control panel 20 communicates with each of the detection devices 181 . . . 18N, keypad 25 and personal device 19 as well as with an offsite monitoring service 30 which is typically geographically remote from the monitored premises in which system 10 is installed. Control panel 20 may include a CPU 34, memory 35, and communicator 36. CPU 34 functions as a controller to control the various communication protocols within system 10. Memory 35 stores system parameters, detection device information, address information, etc. Communicator 36 sends and receives signals to/from the monitoring facility 30 via communications link 31. Alternatively, communicator 36 may be a separate device that communicates with controller 20 via a hardwired or wireless connection.
Generally, when an alarm condition occurs based on the operation of one or more detection devices 181 . . . 18N, a signal is transmitted from the respective detection device to control panel 20. Depending on the type of signal received from the one or more detection devices, communicator 36 communicates with monitoring service 30 via link 31 to notify the monitoring service that an alarm condition or anomaly has occurred at the premises. Communication link 31 may be a POTS (Plain Old Telephone System) connection, a broadband connection (e.g., Internet), a cellular link such as GSM (Global System for Mobile communications) transmission, satellite communication, etc. In certain security systems, keypad 25, control panel 20 and communicator 36 may be housed within a single unit.
For wireless communication, the keypad 25, control panel 20, communicator 36, and detection devices 181 . . . 18N each include an antenna for transmitting and receiving signals. These antennas are formed on a surface of a printed circuit board (PCB) on which the other electronics of the security system may be disposed. One example of such an antenna is an inverted-L antenna (ILA). ILAs may be re-tuned by changing reactive feed components such as discrete inductors and capacitors. However, ILAs have a directional radiation pattern, which is not desirable for security systems as it requires a precise installation of the various receivers and transmitters such that communication between the different components is possible.
Another example of an antenna is an inverted F antenna (IFA), which has a more favorable omni-directional radiation pattern compared to ILAs. However, conventional IFAs are incapable of tuning without changing the physical layout of the antenna on the PCB. For example, FIG. 2 illustrates an IFA 100 including a ground plane 102 and a radiating element 104 extending from ground plane 102. Radiating element 104 includes a ¼ wavelength radiating portion 106 disposed adjacent to an impedance tap point 108 where a feed line 110 intersects radiating element 104.
The impedance of IFA 100 is determined by the placement of impedance tap point 108, i.e., where feed line 110 intersects radiating element 104, along the length of radiating element 104. For example, placing feed line 110 such that tap point 108 is electrically closer to the ground plane 102 along ¼ wavelength radiating portion 106 decreases the impedance whereas placing feed line 110 in an opposite direction along the radiating element increases the impedance. Consequently, impedance adjustments to conventional IFAs require new PCBs to be fabricated or spun in order to place the feed line 110 at the desired point along radiating element 104.
To adjust the resonant frequency of an IFA, the length of the radiating element is shortened or lengthened. This also requires the fabrication of a new PCB on which the antenna is disposed. This limitation of conventional IFAs requires security system providers to develop separate PCB designs for various systems. For example, in systems installed in North America, signals are transmitted with a frequency of approximately 433 MHz. This requires an IFA configured for this frequency. Systems installed in Europe require signals transmitted with a frequency of approximately 868 MHz. Consequently, a different IFA configuration is required for this frequency. Accordingly, an improved planar IFA design is desirable that may be configured for various impedance and frequency transmissions.